The present invention relates generally to providing pressurized air and electrical power to perform various functions on a vehicle such as an aircraft. More particularly, the invention relates to systems which eliminate a need to extract bleed air and reduce extraction of electrical power from main engines of the vehicle.
Future aircraft, including future main engines and future subsystems, are being developed to achieve ever increasing levels of fuel efficiency to reduce the cost of travel while at least maintaining if not improving safety and dispatch reliability. Aircraft engine and subsystems all need to be designed such that they work together to collectively enable this overall fuel efficiency improvement. More efficient engine cycles will continue to drive core flows down by pushing engine pressures and temperatures up. This has made both traditional bleed architectures and no-bleed, more-electric architectures increasingly difficult to integrate with subsystem loads. Bleed architectures have been more difficult because the required bleed air flows for environmental control systems (ECS) are a larger percentage of the total available main engine core flow. Also bleed flow temperatures in the bleed air systems, especially in valves between main engine and pre-coolers and in the pre-coolers themselves, have become more difficult to manage. Therefore consideration has been given to in-flight operation of an auxiliary power unit (APU) to offload large bleed air and or electric loads from the main engines. If such in-flight operation of an APU could be successfully implemented, the main engines could adopt more efficient cycles without being as constrained by the bleed and or electric power interfaces.
But this approach has not been adopted by any major platform at least partly because of challenges arising from obtaining efficient APU performance during both ground and in-flight conditions. Additionally there has not been an effective system devised to meet certification and safety in the event of an in-flight APU failure.
In more electric aircraft, electrical redundancy is typically provided by configuring each main engine with multiple generators. This multiplicity of main-engine generators results in substantial undesirable increase in weight of the aircraft.
As can be seen, there is a need for supplying pneumatic and electrical power on a vehicle without employing main engine energy. Also, there is a need for a power architecture in which operation of an APU is a principal source of pneumatic and electrical power. Still further, there is a need for such an architecture in which failure of the APU can be tolerated within certification and safety standards without incurring a need for a multiplicity of main-engine generators.